1. Field of the Invention (Technical Field)
The present invention relates to a gravity-balanced passive apparatus and method to physically simulate perambulation such as walking, hopping, jogging, running, or other movements in reduced gravity condition.
2. Description of Related Art
The design of balancing apparatuses has been an active research topic for several decades. The problem of static and dynamic balancing of linkages has been studied extensively in the past. Static balancing of an apparatus occurs when the links and payload do not exert any torque or force on the joints of the apparatus at any configuration of the apparatus. This condition is also referred to as passive gravity compensation.
Many gravity-compensated serial and parallel manipulators have been designed using counterweights, springs and sometimes cams and/or pulleys. A hybrid direct-drive gravity-compensated manipulator has also been developed. Moreover, gravity-balanced leg exoskeletons used for assisting persons afflicted with hemiparesis to walk have been studied.
Two basic approaches exist for static balancing, namely, using counterweights or using springs. An apparatus has the property of maintaining its mass center at a globally fixed location when using the counterweight approach. Static balancing is achieved in any direction of the Cartesian space of the apparatus. This property is useful for applications in which the apparatus must be statically balanced in all directions, e.g. if the apparatus is to be installed in an arbitrary direction with respect to the gravity acceleration vector. However, the drawback of this balancing method is that additional weights must be added to the system which results in larger inertia forces because of the added mass of the system.
Alternatively, when springs are used for static balancing, the total potential energy, i.e. the gravitational potential energy plus elastic potential energy of the apparatus is maintained constant and the weight of the entire apparatus is balanced with a much smaller total mass than when using counterweights. However, a spring-based balancing apparatus balances only along the direction of the gravity vector, which is unsuitable for some applications.
In space exploration missions, astronauts are often required to perform extra-vehicular activities (EVA). Such activities occur either in a microgravity environment such as on the International Space Station (ISS) or in a reduced-gravity environment such as on the Moon or Mars. To ensure the success of a mission, extensive training is required for the astronauts before a real mission is launched. Astronauts usually spend more than ten times the real EVA time in a ground-based microgravity training facility such as a neutral buoyancy pool when practicing a planned EVA task. Therefore, the training technology and facility have a significant impact on the quality, cost, and time of the required training.
Several existing technologies can be used for EVA training in a simulated reduced gravity condition, such as a neutral buoyancy pool, parabolic-trajectory flight, counter-weight suspension; air-bearing/gimbal support, and virtual reality. All of these technologies have drawbacks when used for physical simulation of reduced gravity conditions. For example, the parabolic-trajectory flight technique can simulate zero-G for only 20 to 30 seconds and thus is too brief for training most of the EVA tasks. The counterweight balanced suspension method can effectively provide only one-degree-of-freedom controlled motion in the vertical direction. The other degrees of freedom are either constrained or do not match motion as it actually occurs in space. An air-bearing supported system performs 2-D or preudo 3-D simulation only. The virtual reality simulations provide a visual effect without much real physical reaction. The neutral buoyancy technology which is the most commonly used existing technology suffers from water viscous drag, sealing problems, and an onerous burden of multiple safety measures.
Existing reduced-gravity simulation technologies either cannot generate a full range of physical motion in space or cannot be easily or economically accessed. Therefore, there exists a need for developing alternate methods for reduced-gravity simulation which are inexpensive and which are easily implemented.